Re: [PATCH] PM: Make it possible to avoid wakeup events from being lost

[Rafael J. Wysocki]

On Friday, July 02, 2010, Pavel Machek wrote:
> On Thu 2010-07-01 21:02:27, Rafael J. Wysocki wrote:
> > On Thursday, July 01, 2010, Pavel Machek wrote:
> > > Hi!
> > > 
> > > > @@ -114,3 +114,17 @@ Description:
> > > >  		if this file contains "1", which is the default.  It may be
> > > >  		disabled by writing "0" to this file, in which case all devices
> > > >  		will be suspended and resumed synchronously.
> > > > +
> > > > +What:		/sys/power/wakeup_count
> > > > +Date:		July 2010
> > > > +Contact:	Rafael J. Wysocki <rjw@xxxxxxx>
> > > > +Description:
> > > > +		The /sys/power/wakeup_count file allows user space to avoid
> > > > +		losing wakeup events when transitioning the system into a sleep
> > > > +		state.  Reading from it returns the current number of registered
> > > > +		wakeup events and it blocks if some wakeup events are being
> > > > +		processed at the time the file is read from.  Writing to it
> > > > +		will only succeed if the current number of wakeup events is
> > > > +		equal to the written value and, if successful, will make the
> > > > +		kernel abort a subsequent transition to a sleep state if any
> > > > +		wakeup events are reported after the write has returned.
> > > 
> > > I assume that second suspend always succeeds?
> > 
> > The mechanism is one-shot if that's what you're asking for.
> 
> Yep, it would be nice to document it.
> 
> Plus maybe... should there be way to clear the wakeup_count? For
> example when userspace decides that battery is low and that it wants
> to go to sleep now?

You don't need to clear it, just don't write to it before writing to
/sys/power/state.

Rafael
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